The invention relates to controlling the flying height of a magnetic recording disk drive; and, more specifically, the invention relates to preventing a crosstalk against the read head.
A conventional magnetic recording disk drive (hereinafter referred to as HDD) comprises a head/disk assembly that is a mechanical system, and a package substrate (PCB) made of circuits. FIG. 13 shows the configuration of a head/disk assembly (HDA) 100. The HDA 100 comprises components such as: a magnetic recording disk 2 installed in a chassis (base) 8 through a spindle 5; a magnetic head assembly 1 mounted on the tip of a suspension 3 connected with an actuator 4 driven by a voice coil motor (VCM) 7; a flexible printed cable (FPC) 6-3 having mounted thereon a read/write IC (R/W IC) 11 which electrically drives the magnetic head assembly 1. The actuator 4 moves the magnetic head assembly 1 so as to position it at an arbitrary location while the magnetic disk 2 is being rotated at a constant speed before the write/read operation begins.
FIG. 14 shows how the magnetic head assembly 1 is suspended above the magnetic recording disk 2 in a read/write operation. Due to increasing recording density of a magnetic recording disk drive, reduced flying hht of the magnetic head is required. With a reduced flying height, however, the write head element (WRT) 1-2 or the read head element (RD) 1-1 is likely to collide with a small bump 51 with a height of a few nanometers. These bumps are formed due to, for example, the surface roughness of the magnetic recording disk 2.
The flying height of the magnetic head assembly above the magnetic recording disk 2 is set to a small value, for example no more than 20 nm, in recent years. Assume that the small bump 51 has collided with the read head element (RD) 1-1. In such a case, if the RD 1-1 is a magnetoresistive head (hereinafter referred to as an MR head), the element produces heat and thereby an abnormal signal is generated by a thermal asperity (hereinafter referred to as TA) event. Such an incident results in a read abnormality. Further, when a high-frequency write current of a few hundred megahertz flows through the write head element (WRT) 1-2, the element produces heat and thereby the rear end of the magnetic head assembly projects toward the disk surface, as indicated by the broken lines in the figure. The higher the frequency of the high-frequency current, the larger the projection amount, reaching a few nanometers or more, due to the heat produced by the eddy current. With a reduced head flying height, a head element of the magnetic head assembly might be damaged if it protrudes.
FIG. 15 shows wiring (FPC) 6-1 on the suspension 3 for a magnetic head assembly implemented by a prior art that does not use a resistive heating element HEAT 1-3. A crosstalk current flows through wires RxX and RxY on the RD side due to the high-frequency current flowing through wires WxX and WxY on the WRT side and the flyback voltage in the write operation. The sense current supplied to the read head 1-1 is generally between 2 mA and 3 mA, and if the WRT side and the RD side are in close proximity, the crosstalk current might be as large or larger than the sense current. Since the read sensitivity increases with increasing sense current, the sense current is preferably set as large as possible within the allowable range. Further, at the same time, long life duration is required.
However, in case of a crosstalk, the value of the sense current must be reduced. Therefore, the wires on the WRT side are disposed away from the wires on the RD side to reduce the crosstalk current, and thereby increase the allowable value of the sense current. Also, an alternating current against the MR element of the read head, which is caused by the crosstalk current from the WRT side to the RD side leads to a reduction in the life duration of the MR element itself.
One technique used to solve the above problems is to install the resistive heating element HEAT 1-3 near a head element whose flying height has been increased beforehand, as shown in FIG. 14. With this arrangement, the protruding action of the head element due to heat from the resistive heating element HEAT 1-3 is rather utilized in order to control the flying height of the head element (see Japanese published application JPA 5-020635). There are various ways in which this resistive heating element is used. Generally, however, a current is passed through the resistive heating element in the read operation so as to reduce the flying height of the head element by using the heat produced by the resistive heating element. In the write operation, on the other hand, the current to the resistive heating element is basically cut off since due to the high-frequency write current flowing in the write operation, heat is already being produced, reducing the flying height. However, an appropriate amount of current may be applied in a low-temperature environment such as when the equipment is started. Alternatively, a low current may be applied all the time while adjusting its magnitude in order to provide some narrow flying height.
Another proposed prior art technique is to implement a magnetic head assembly which includes a heating magnetic head in addition to the write magnetic head and the read magnetic head (see Japanese published application JPA 11-096608). The technique disclosed in Japanese published application JPA 11-096608 increases the temperature of a recording portion of the recording medium to a value corresponding to the write or read temperature in the write or read operation by use of the heating magnetic head, making it possible to read from or write to narrowed tracks.
However, in Japanese published application JPA 5-020635, neither the detailed means nor the circuit configuration for controlling the amount of the generated heat is disclosed.
Furthermore, if new wiring is provided on the FPC 6-1 to supply power to the HEAT 1-3 in the prior art technique shown in FIG. 15, it may be necessary to reduce the distance between the wires WxX/WxY on the WRT side and the wires RxX/RxY on the RD side. This might result in an increase in the crosstalk current. Increased crosstalk current leads to reduction of the sense current to ensure adequate head life duration, which is not preferable. Further, the power supplied to the resistive heating element HEAT 1-3 is a maximum of a few ten milliwatts. Assuming that the resistance of the HEAT 1-3 is between some ten ohms through some hundred ohms, the current and the voltage amount to some ten milliamperes and a few volts, respectively. Therefore, if the current supplied to the HEAT 1-3 is switched on/off while data on a magnetic recording disk or a servo signal is being read, a large crosstalk current flows through the wires on the RD side, which can cause an abnormality in the read operation.
On the other hand, the heating magnetic head described in Japanese published application JPA 11-096608 is provided to increase the temperature of the recording media; it is not intended to control the flying height of the magnetic head. Furthermore, no consideration is given to the adverse effect of a crosstalk current against the read magnetic head, which is caused by switching the current on/off in the heating magnetic head, or by the high-frequency write current of the write magnetic head.